Notice that Alma equates this apostasy from the church to “the destruction of the people.” This is a theme that he has raised in the past:
Alma 1:12 But Alma said unto him: Behold, this is the first time that priestcraft has been introduced among this people. And behold, thou art not only guilty of priestcraft, but hast endeavored to enforce it by the sword; and were priestcraft to be enforced among this people it would prove their entire destruction.
In this verse Alma is discussing Nehor, but the teachings of Nehor are essentially those that the Amlicites adopted, and are most likely those that are leading to the wearing of “costly apparel” and that accompanies that sin. Alma indicates that these teachings would lead to their “entire destruction.”
Similarly, Alma notes:
Alma 3:8 And this was done that their seed might be distinguished from the seed of their brethren, that thereby the Lord God might preserve his people, that they might not mix and believe in incorrect traditions which would prove their destruction.
The mixing with the Lamanites would lead to believing what the Lamanites believed, and that would “prove their destruction.” Clearly, what Alma is referring to is not the physical eradication of the people, but a loss of their culture/religion. In believing as the Nehors, or believing as did the Lamanites, the Nephites would have to abandon their religion which was their way of life. With the removal of this religion that holds them together, they would be effectively destroyed as a separate people.
This fear of destruction through the adoption of the ways of the world is not unique to Alma. We find a similar fear in Enos:
Enos 1:23And there was nothing save it was exceeding harshness, preaching and prophesying of wars, and contentions, and destructions, and continually reminding them of death, and the duration of eternity, and the judgments and the power of God, and all these things—stirring them up continually to keep them in the fear of the Lord. I say there was nothing short of these things, and exceedingly great plainness of speech, would keep them from going down speedily to destruction…
It has been a characteristic of the Nephites from the earliest times that they were seduced by the ways of the world. Ultimately, the adoption of those ways would destroy them as a separate people.